It is ABSURD to think that something as unspecific to running as weight training like squats, deadlifts, etc (where one is on 2 feet, with feel split apart, deeply bending one's hips......all elements that do NOT occur when running) can help running but something as specific as weighted running could not. Absurd. And I don't think that classic weight training like squats etc do not help. No, I think they do. But that is GENERAL strength training/conditioning. Again, if that helps, why on earth would something as specific to running as running up a hill with weighted vest for 50 m not potentially help?
And running on a decline is NOT "assisted running" just as running up a hill isn't resisted running, right Alan? You can't have it both ways. And if you are going to dismiss running with weights, I've read several studies denouncing the positive effects of assisted running. Two can play at that game (just because something hasn't been proven beyond any doubt to help, doesn't mean it might not. Not all studies are perfect. So I think assisted (like Alter G) or resisted running can both have potentially positive effects if done right).
To answer the OP's original question: running all or most or even a lot of one's workouts in a weighted vest would be dumb. Used occasionally and judiciously it could help. Be strength trained previously, only add very small amounts of weights at first, even just do walking. And gradually build up to some short sprints with moderate weights. Anything that causes you to feel awkward or change your stride would be bad.